Mark's Stuff

On the 13th of May 2009, Kirsty and I welcomed our daughter, Pia Grace, into this world. She was supposed to arrive mid-June, but was obviously in a bit of a hurry! She weighed in at a small 2.09kg, and will hopefully be able to come home with us in a few days time.

Kirsty and I have been spending a bit of time in the special care nursery at the hospital (Kirsty much more than me), and Pia is slowly building up the stamina to last a full feed before falling asleep!

Due to excessive badgering by friends and family alike, I’ve uploaded a few more pics in my new Family gallery.

Well I guess it should be fairly obvious.. you shouldn’t drive it upside down! We came across this unfortunate scene just outside The Rip at Port Phillip Heads en route to dive the Rotomahana. We’re unsure exactly how it happened, but suspect it was the driver trying to pull the anchor up while it was attached to the stern of the boat. Add to that an oversized 250HP outboard on the back, and the owner is lucky that the boat was eventually righted and towed to shore. We offered some assistance by way of a couple of divers suiting up and jumping in to try and free the anchor line, but eventually let the water police (nice jetskis, eh?) and port authorities take care of it, and we headed off to the Rotomahana.

The SS Rotomahana lies in about 40m of water, and although there is not much left of her, she still boasts two massive boilers which make for a cruisey little swim through, and there’s still quite a bit of the deck structure remaining, albeit rather broken up. And of course abundant fishlife. But at 40m, and Justin and I not diving with a deco mix, we had about 20 minutes bottom time, a 10 minute ascent to 6m, and a further half hour of thumb twiddling at the shot-line washing off deco obligations.

After the Rotomahana, next stop was a quick drop-off at Portsea for a fill, while Ocean Diver headed back to Sorrento to pick up some more passengers for Anchor Wall and he Arches. The wind and swell picked up a bit so after Anchor Wall we couldn’t head back outside the heads. The alternative was a rather slow scallop drift just off Rye. Having never had the urge to take a photo of a scallop before, I took this pic which shows quite nicely how this stingaree and scallop have buried themselves for camouflage from natural predators. Like divers.

And as usual, a few more pics in my Melbourne Diving gallery.

After much talk, and further proscratination disguised as “finalising the design”, I finally convinced myself to take a couple of weeks off work to build a deck out the back of our house.

Armed with a truckload of treated pine and merbau, a few hundred galvanised framing nails, a box of 2000 stainless steel screws, a power drill, two cordless drills, a circular saw, a jigsaw, a drop saw, two saw horses, framing gun, chalk line, laser level, sprit levels, line level, tape measure, two shovels, a pick, one hired post hole digger (broken), one hired post hole digger (working) and a 4m² skip, my dad I got to work.

Day One was marking out all 19 post holes, digging them cleaning them out and setting up string line stakes for when the posts got put in.

Day Two had us waiting around for the concrete to be delivered. It was scheduled for midday, and by 10:30 we had double checked as much as we could, so got to demolishing the front brick fence while we waited. The concrete turned up around 12:30, and we had 20 minutes to barrow almost one cubic metre from the truck around the back and fill up the holes. String lines went up, the posts stuck down into their holes, and we called it a day while waiting for the concrete to set.

Day Three was Framing Day. Five bearers, and eighteen joists later and we had a (pretty much) perfectly level footing to work with.

Day Four was a lazy start waiting for the merbau to arrive. It turned up just after lunch, and we only managed to lay 5 rows of decking before the umpire called stumps due to bad light.

Days Five to Eight had as doing the same over and over. Choose a “random” length of merbau so that the joins were well spaced out, bevel the end, find a suitable matching piece, bevel the end. Lay them down, measure against a chalk line, adjust spacing, drill and screw. Repeat for 63 rows of decking, to lay a total of 390 linear meters. With a rest day in between.

The last day of deck laying also included making a frame for the BBQ to sit on, and finishing up the base boards making up the edge of the deck. A plumber was enlisted to hook up the barbie to natural, then a couple of coats of Cabot’s Aquadeck for protection, a quick trip to Ray’s Outdoors for some furnishing, and we’re ready for entertaining!

The only outanding thing now is to find a suitable sink to install next to the BBQ. Hot and cold water and waste are ready to be hooked up, there’s nothing to hook them up to yet

Oh, and I suppose it would be nice to get some nice real grass out there instead of the rollout plastic stuff covering up the dirt at the moment!!

After many failed attempts at findind a suitable, cost effective, amplifier solution to drive all the ceiling speakers throughout our house I decided to finally give up and make my own.

So I got a hold of two 25W amp kits based on an LM1875 IC, and a power supply suitable to drive both of them.

Below are pictures of firstly the power supply driven by a 160VA 18-0-18V toroidal transformer, and secondly of the two amps mounted together and attached to the heatsink on the rear of the case. Each transformer can comfortably drive 4 x 25W amps.

The case is just a cheap 19″ rack mount enclosure from Jaycar which is quite easily customisable with adjustable mounting rails, and is pretty solid once assembled. As you can see below, plenty of space for another 3 power supply circuits and 6 amps, to make the unit up to its capacity of 8 channels. I could potentially squeeze in another 2 channels, but then heat starts to become more of a problem, as does finding rear panel space for connectors.

Yes, I know the heatsinks aren’t straight.

Add four dual 50kΩ log pots for stereo volume controls, a power switch and LED on the front, and the amp is ready to go. Well, except for the fact that there’s only 2 out of 6 channels built so far.

The biggest challenge of this project was eliminating the hum that I first heard when I turned it on. I knew the electronics were fine, as the amp was very quiet when I first tested it outside the casing. The hum was very much indicative of interference, likely caused by a ground loop.

The first step was to change the wire from the input terminal, to the pot and then to the amp. I made the mistake of using cat6, as it conveniently has the right number of wires. But no good for unbalanced audio. The noise reduced significantly after replacing it with shielded coax. But it was still there.

I soldered in extra ground wires, I tied the ground to the mains earth, I moved wires away from the transformers, all to no avail. Then eventually when probing around with the multimeter, I accidentally shorted out the negative input signal wire to the casing of the volume pot, and the instantly disappeared. Now I have zero hum all through the volume range. And the 25W/ch is plenty for the ceiling speakers. Not sure about driving outdoor speakers for the deck (when it gets built), so I may need to make a 2×50W amp for those.

Next step is to introduce a microcontroller to drive volume and turn channels off by relay (power saving) via RS232.

This Queen’s Birthday Weekend I headed up to Mt. Gambier to finish off my last required dive for my CDAA Deep Cavern certification, which I completed in Little Blue on Friday morning. On Saturday Jake and Ellen took me on a guided tour of Piccaninnie Ponds, which was a treat after fudging around in the 1m visibility of Little Blue. Jake and I dropped into Ewen’s Ponds after that, but unfortunately on the tail end of about 20 other divers, so the water was a little stirred up.

My weekend finished on Monday morning at Kilsby’s, with this trip’s second awesome dive at that hole in the middle of a sheep paddock. I tagged my camera along for a couple of the dives, but my photos just don’t do the dives justice. Definately more practice required at this sort of photography. And maybe another strobe wouldn’t hurt either!